1. Field of the Invention
The present invention relates generally to blood filters and more particularly to a blood filter as may be used in cardiopulmonary bypass surgery having an improved system for removing gas bubbles from the blood.
2. Description of the Prior Art
With the increased frequency of cardiopulmonary bypass surgery and with the recognized need for delivering gas free blood back to the patient, numerous blood filters have been developed. Such filters are used in connection with pump-oxygenator equipment commonly referred to as heart lung machine that are used during open heart surgery. Such surgery, requires that the blood of the patient be shunted around the heart and lungs permitting the surgeon to operate on a heart, whose chambers are relatively free of blood. In operations of this type, it is absolutely essential that all excess gas be removed from the blood before it is returned to the patient or fatal air embolus can occur.
Most filter devices developed for use in cardiopulmonary bypass surgery include a filter screen or mesh of a predetermined size to filter out undesirable elements including gas bubbles whether in the form of micro emboli or gross bubbles. In addition, the housings for some such filters have been designed to further encourgage the removal of gas bubbles. For example, in the U.S. patents issued to Johnson & Johnson/Purolator, Inc. U.S. Pat. Nos. 3,939,078, 4,038,194 and 4,046,696, the concept of abruptly decreasing the flow rate of the gas as it enters the filter to release entrained gas is disclosed. Further, these patents disclose the use of a slanted upper wall in the housing to direct gas released from the blood to a vent port in the upper wall. In one of these patents, namely U.S. Pat. No. 3,939,078, the blood inlet to the filter device extends downwardly from the slanted upper wall so as to keep the inflow of blood separate from the gas being removed therefrom which further improves the efficiency of the gas removal by preventing the incoming blood from being mixed with the gas removed from prior blood. U.S. Pat. No. 4,676,771 issued to Henke also broadly recognizes that abruptly slowing the flow rate of blood encourages the release of gas. It will therefore be recognized that ongoing efforts are being exerted toward improving the efficiency with which gas bubbles can be removed from blood before the blood is returned to a patient to diminish the possibility of fatal air embolus.
While the structural features shown to date in the prior art provide improvements over the mere use of a filter medium to remove gas from the blood, it is felt that more efficient systems would be desirable and it is to this end that the present invention has been developed.